In brief: A lot of movies suggest that diving into water is a good way to escape gunfire, but that's no protection against new bullets being tested by the US military that can move swiftly and at great length through liquids.
Created by Virginia’s DSG Technologies, the tungsten-tipped bullet works by creating a gas bubble as it moves through water. As Defense One reports, this massively reduces the amount of drag—a supercavitation effect that’s also used in torpedos and some boats. As standard bullets don’t have this effect, friction slows down their velocity, and they quickly stop when traveling through dense liquid.
U.S. Special Operations Command, or SOCOM, is reportedly putting the bullets through various tests, one of which involves shooting them up toward the surface from underwater. Odd Leonhardsen, DSG's chief science officer, said the bullets are being sold to other governments. While he never named them, he did say they were testing to see how the bullets performed when fired from helicopters into water, suggesting they could be used against submarines. Tests show the 50-caliber bullets can travel 60 meters through water or penetrate 2 cm of steel through 17 meters of water.
“This projectile is effective against submerged targets and targets in the air. Depending on the weapon and the used loading variant, this ammunition is suitable for use in partial or fully submerged weapons, regardless of if the target is in water or on the surface,” said DSG Technologies.
Exactly how these bullets create a gas bubble is unknown, but Popular Mechanics believes that they somehow use the gases from the burning gunpowder. Additionally, the ammo will work with existing weapons, and can also penetrate sandbags and body armor.